In the field of automobiles, as the approach to the environment, weight reduction of the vehicle body by metal substitution has been demanded for reduction of the emission. For this purpose, polyamide resins have been progressively employed for exterior materials and interior materials. Especially, accompanied with a temperature increase in the engine room, further improvement in heat resistance has been demanded for the polyamide resin used for the relevant parts. The polyamide resin has hydrophilic amide groups and accordingly has a problem of dimensional change caused by absorption of water.
In the field of electricity and electronics, on the other hand, along with development of lead-free systems and popularization of surface mount (SMT) there has been a demand for the polyamide resin of the high heat resistance that can withstand the high temperature treatment in the reflow oven. Another problem of the polyamide resin is the appearance of blister (air bubbles) in the reflow process, due to water absorption of the polyamide resin.
Additionally, as the adverse effects such as climate change accompanied by global warming have been addressed, reduction of carbon dioxide has been demanded and plant-derived plastics have attracted attention.
Patent Document 1 discloses a production method of a polyamide resin obtained by polycondensation of an aliphatic diamine as a mixture of hexamethylene diamine and 2-methylpentamethylene diamine and an aromatic dicarboxylic acid selected from, for example, terephthalic acid and isophthalic acid. Patent Document 2 discloses a polyamide resin that includes, as primary components, a terephthalic acid derivative and an aliphatic diamine mainly comprised of pentamethylene diamine which is manufactured from a plant material and hexamethylene diamine. Unlike 2-methylpentamethylene diamine, pentamethylene diamine is a symmetrical molecule with no substituent group in its side chain. A polyamide resin obtained from pentamethylene diamine has excellent crystallinity and is thus likely to precipitate in the course of polymerization. It has accordingly been regarded as difficult to achieve high polymerization by only melt polymerization. Patent Document 3 also discloses a polyamide resin that includes, as structural components, pentamethylene diamine and terephthalic acid or its derivative. Patent Document 3 employs solid phase polymerization as the production method of a crystalline polyamide resin having a melting point of or above 270° C. Additionally, in the case of polymerization of a polyamide resin using a highly hydrophobic compound such as diaminononane or diaminodecane as at least part of the diamine component, there is also a problem that polymer is likely to precipitate in the course of polymerization of the polyamide resin in the presence of water, due to the high hydrophobicity of the above diamine component.
Patent Document 4, on the other hand, discloses a polyamide resin that includes, as structural components, pentamethylene diamine, terephthalic acid and sebacic acid. Additionally, Patent Document 5 discloses a polyamide resin obtained by polymerization of an alicyclic dicarboxylic acid and a diamine including a diamine having a pentamethylene diamine skeleton. The polyamide resin using pentamethylene diamine specifically described in these patent documents has a small content of terephthalic acid relative to the gross amount of the dicarboxylic acid component or a small content of an alicyclic dicarboxylic acid relative to the gross amount of the dicarboxylic acid component and has the low crystallinity. Accordingly there is little possibility that polymer precipitates in the course of polymerization.